Engine Rebuild Pickle

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Ok so I'm in a pickle. I need to rebuild the engine in the XJ. It gets god awful gas mileage, runs super rich, I know the exhaust valve is bad in cylinder 3, and misfires. It still runs and drives but needs help before winter since it's my winter driver.

I'm trying to decide what all to do and could use advice from guys who have done an at home rebuild. I want to avoid taking it to a shop at all costs, I'd rather sell it as is than pay for shop labor and such. Id also rather do a rebuild than engine swap because I want to learn to rebuild plus Id rather not chance a junkyard motor without rebuild. Buying full rebuilt motor isnt going to happen either.

I know the head needs rebuilt or replaced but know nothing about the bottom end.

Question for the head, should I rebuild the entire head, just replace what needs replaced, or buy a reman? I'm leaning reman because I can't check for cracks at home and it would be way less work for me. Plus do you have to have the surface machines before reinstall of old head?

If I rebuild the bottom end I'd go the dingleball route. If doing that do I just ream the ridge and hone then drop in the stock replacement pistons and rings? I've seen this done on Roadkill but not sure if that's the "approved" dingleball process.

I've got the rebuild book on the 4.0 and I've done a bunch of reading and watching videos but everything talks about the proper way of doing machine work. Basically what's the "proper" at home dingleball route for a stock rebuild?

Or do I do some upgrades in the process but still keep it budget friendly..

What's your guys thoughts and experience?

PS I suppose this could have gone it tech, not really sure why I did pub.

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At a minimum you should get the heads and block machined. I wouldn't try and DIY that part. Especially if you don't have any of the proper tools. Not worth the chance of messing it up. For the heads I would just let the shop do it all and give you a "drop in ready" unit. Whether that's a core exchange or rebuilding your current one.

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At a minimum you should get the heads and block machined. I wouldn't try and DIY that part. Especially if you don't have any of the proper tools. Not worth the chance of messing it up. For the heads I would just let the shop do it all and give you a "drop in ready" unit. Whether that's a core exchange or rebuilding your current one.

Yeah the head is a little more involved and I would have to buy most of the tools making a drop in unit cheaper.

Say I do nothing with the bottom end, could I drop a reman head on it without having the block decked? I don't see why I wouldn't be able to but worth asking I guess.

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You are right on work the dingle ball and ridge ream. I had an uncle who did this all the time. Knock off the ridge on top and dingle ball until the cylinders look good. I would definitely just take the head to the machine shop. Have them check it and do a valve job. Then just reassemble. That is unless you have deep acting in the cylinders then you will need to over bore.

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Yeah the head is a little more involved and I would have to buy most of the tools making a drop in unit cheaper.

Say I do nothing with the bottom end, could I drop a reman head on it without having the block decked? I don't see why I wouldn't be able to but worth asking I guess.

You should be able to put a reman head on without touching to bottom end. I wouldn't quote me on that one though.

In the end it's all personal preference really. I would just look at it as you are already going through the work, time and money to do it and if it's a difference of a few hundred bucks to be done and done right. I hate doing double work. So if I'm already going through the trouble of doing something most times I just opt to do it once and right, but I get sometimes it's not in the cards.

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You should be able to put a reman head on without touching to bottom end. I wouldn't quote me on that one though.

In the end it's all personal preference really. I would just look at it as you are already going through the work, time and money to do it and if it's a difference of a few hundred bucks to be done and done right. I hate doing double work. So if I'm already going through the trouble of doing something most times I just opt to do it once and right, but I get sometimes it's not in the cards.

I really just need to get through another winter, maybe 2 before I can afford the daily driver I want without having 2 large car payments. I've got some other home improvement projects that need done so I don't want to sink more than $1000 or so into this. All it needs is tires (probably getting the ones from my red truck) shocks, and engine rebuild.

If I can do it cheaper it just means I can get other stuff done sooner like lowering the red truck..

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I'll have to redo them. I checked 2 years ago and the oil pressure was good but cylinder 3 had low compression, something like 95psi iirc. The exhaust sucks in during the misfire which is what tells me it's got an exhaust valve problem.

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Look on craigslist or facebook marketplace for a used 4.0L engine. Usually around here is $300-$400. Have proof it ran and such, (good) then when your engine that's in the truck now is out, rebuild it and do it right.

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My vote is pull the head, have it gone through or slap a good used one on and wait the year or two.

I'm leaning more and more towards this. I really don't know what the bottom end looks like and won't know until I tear into it. Maybe just rebuild top end and replace oil pump and reseal bottom.

The motor has roughly 170k miles on it so it shouldn't be terrible, then again it shouldn't have had a valve issue either. This Jeep was really not well taken care of so I could find anything in there.

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You can get away with a lot if you just want it to run for another year or two.

I once bought a well-abused old Javelin for $50 when my daily driver had been injured in an accident and I needed wheels. The Javelin I-6 engine was the predecessor for the Jeep 4.0L. The one I got had been sitting for so long the valves were sticking and the pistols were stuck in the bores. I pulled the head, got the valves loose, cleaned them up on a wire wheel and just re-lapped them onto the seats.

I used a length of 2x3 to knock the pistons loose after soaking with penetrating oil. I reamed the carbon ridges,, rotated the pistons as far down as they would go, honed the cylinder walls, wiped them down with assembly lube, and put everything together with a new head gasket. No new pistons, not even new piston rings. It ran just fine for two years, after which I sold it for more than I had paid for it.

What's your budget, and what do you really want out of this rebuild/whatever?

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You can get away with a lot if you just want it to run for another year or two.

I once bought a well-abused old Javelin for $50 when my daily driver had been injured in an accident and I needed wheels. The Javelin I-6 engine was the predecessor for the Jeep 4.0L. The one I got had been sitting for so long the valves were sticking and the pistols were stuck in the bores. I pulled the head, got the valves loose, cleaned them up on a wire wheel and just re-lapped them onto the seats.

I used a length of 2x3 to knock the pistons loose after soaking with penetrating oil. I reamed the carbon ridges,, rotated the pistons as far down as they would go, honed the cylinder walls, wiped them down with assembly lube, and put everything together with a new head gasket. No new pistons, not even new piston rings. It ran just fine for two years, after which I sold it for more than I had paid for it.

What's your budget, and what do you really want out of this rebuild/whatever?

Roughly $1000 to rebuild what I can, new battery, and throw new shocks on maybe. It only gets driven for winter so as long as it starts everytime and gets better than 10mpg I'm fine with it.

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I'll have to redo them. I checked 2 years ago and the oil pressure was good but cylinder 3 had low compression, something like 95psi iirc. The exhaust sucks in during the misfire which is what tells me it's got an exhaust valve problem.

I haven't done leakdown on it as I don't have an air compressor.

This tells me it has an internal issue and I believe it to be exhaust valve cylinder 3. The running rich could certainly be another issue but I don't want to spend all kinds of time chasing stuff like that knowing internally it has problems.

When I've got time either tomorrow or this weekend I'll get it into the shop and run some tests on it to see what current results are and check fuel pressure at the rail. It leaks pretty much everything anyway so it needs resealed so inspection makes sense regardless.

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I'm leaning more and more towards this. I really don't know what the bottom end looks like and won't know until I tear into it. Maybe just rebuild top end and replace oil pump and reseal bottom.

The motor has roughly 170k miles on it so it shouldn't be terrible, then again it shouldn't have had a valve issue either. This Jeep was really not well taken care of so I could find anything in there.

Here is my suggestion (having been in your shoes):

Most of your decision should be based on the compression test and oil pressure. However, since you state that you have a trashed valved on one cylinder, at least one of your six compression test readings may be invalid.

If compression on 5 of six is pretty even, and within acceptable limits for age, it's probably a good bet the valve is the cause of the low reading on the remaining cylinder. Once the head is pulled to deal with the valve issues, you can visually examine the low cylinder and confirm it's walls are smooth, and the piston doesn't rock too much. That would indicate that a refreshed head would make all things good in the cylinders, and that would be the route I would do on the top.

If the oil pressure is within the normal range, don't worry about the bottom end. (This assumes you have no funky knocking noises right now.) If the bottom end leaks (pan/RMS), then drop the pan to fix that, and for less than $50, you can throw in a high volume oil pump that would boost pressures on loose bearings a bit. If the bottom is NOT leaking, just leave it be, assuming the oil pressure is OK.